1. Field of the Invention
The present invention relates to a lens member and an optical unit including the lens member, used in, for example, Light-emitting diode (LED) lighting, and the like.
2. Related Art Statement
LED optical products such as lighting, projectors, flash, headlights and tail lamps of automobiles and the like, in which an LED is utilized as a light source, or basic optical devices such as a narrow directivity LED, and so on, generally use a lens for focusing or collimating the light emitted from the LED. Although a convex refractive lens is usually employed for this kind of lens, adoption of a Fresnel lens with the aim of height reduction and thinning is also proposed.
Conventionally, there is proposed a lens for a lamp fitting which has a lattice-shaped refracting prism formed in a central portion of the inner surface near the optical axis, and also has a lattice-shaped reflecting prism formed in a peripheral portion of this lattice-shaped refracting prism (refer, for example, to JP 57-55002 A). In addition, there is proposed a Fresnel lens in which a part of the prisms of the Fresnel lens surface acting as a light-entrance surface is formed such that a part of the entering light rays are emitted from the light-exit surface after being totally internally reflected at the non-lens surface (refer, for example, to JP 59-119340 A). Furthermore, there is proposed an optical device configured from a refractive lens portion having a lens body provided at a central portion of the optical axis and a reflecting body portion, the reflecting body portion allowing light rays to enter from an inner surface portion and totally internally reflecting the light rays at a paraboloid-shaped reflecting surface, thereby converting the light rays into a parallel beam (refer, for example, to JP 05-281402 A).
However, the above-mentioned conventional technology leaves the following problems. That is, in a conventional Fresnel lens, in the case that an edge of a prism is configured with a sharp angle by a prism light-entrance surface and a prism reflecting surface, during resin molding of the Fresnel lens when a metal mold is filled with resin, resin is prevented from reaching the edge of the prism because the edge is narrow or thin. This causes the edge of the prism in its molded state to have a rounded shape. Hence, there is a problem that light-entrance and reflection of light at the rounded edge of the prism cannot be performed with high precision, which results in deterioration of luminance performance in a direction of a central axis AX of the lens member, and so on.
In addition, the lens body disclosed in JP 05-281402 has the disadvantage that its reflecting surface must be high in order to reflect all of the light entering from a rounded shaped light-entrance surface, thereby causing lens thickness to be increased.
Furthermore, the lenses disclosed in JP 57-55002 A, JP 59-119340 A, and JP 05-281402 A have the disadvantage that a loss is generated due to a part of the entering light not reaching the reflecting surface, making it difficult to maximize usage efficiency of the light. For example, in JP 05-281402 A, there is a portion between the light-entrance surface and the refractive lens portion where the entering light does not reach the reflecting surface, resulting in loss of the light passing through this portion.
In addition, when an LED is used as the light source, the radiated light has a light distribution in which the greater the emission angle the smaller the light intensity; therefore, as shown in FIG. 3, when a conventional TIR (Total Internal Reflection) lens 1 is used, the light entering from the light-entrance surface of the inner concave lens portion 3 of the TIR lens 1 disposed to face the light source 2 is totally internally reflected at the reflecting surface of the outer convex lens portion 4; however, this results in the light L2 of relatively strong light intensity in the central portion vicinity being reflected at the reflecting surface at the outer peripheral side of the convex lens portion 4.
Consequently, in this TIR lens 1, brightness in the central vicinity is high, but becomes low in the intermediate vicinity and rises again at the outside. As a result, even if this TIR lens 1 is turned into a Fresnel lens, if a conventional method is used to do so, ring-shaped flare centered on the optical axis is generated in the exiting light which spoils the appearance.
Furthermore, in the lens disclosed in JP 05-281402 A, the light-entrance surface and light-exit surface of the reflecting lens portion are both formed as non-spherical surfaces, and there is therefore a problem that both processing is difficult and costs rise.